Yeah I did that when I cut the slots to make room for the cabin filters (car didn't come with them), thanks to whoever did the DIY!!
You can only get so much out of that tiny space. I almost guarantee that a lot of our evaporators have some form mildew/mold. I did a bunch of research on various cars(domestic, european, japanese) and they are all susceptible to having mold/mildew/bacterial growth which is the main cause of the odors (also if you're a smoker too).
Other than the product I mentioned or other similar products, the only way you can properly get it out is pulling the evap out and giving it a thorough cleaning. I hear it's a pain on some cars, you have to tear the entire dash apart, not sure if it's the same with the R50's.
I just saw this stuff too
http://www.lubegard.com/~/C-204/Kool-It ... am+Cleaner